Semiconductor storage device, semiconductor device, and manufacturing method therefor

ABSTRACT

According to the present invention, a gettering layer is deposited both on the side surfaces and the bottom surface of a semiconductor chip. The semiconductor chip is then mounted on the board of a package so that a Schottky barrier is formed on the bottom surface. With this structure, metal ions that pass through the board of the package can be captured by the defect layer deposited on the side surfaces and/or the bottom surface of the semiconductor chip, and by the Schottky barrier.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device, andparticularly to a thin-film semiconductor chip.

2. Related Background Art

Currently, as the functions provided for cellular phones, digital AVapparatuses and IC cards continue to be improved, there is acorresponding increase in the need for highly integrated, thin andcompact chips that can be mounted in these devices. Thin chips are alsoused in the fabrication of an SiP (System in Package) or an MCP (MultiChip Package), for which a plurality of semiconductor chips are mounted,at high density and in multiple layers, in a single package. Hence, tosatisfy the demand for thin film semiconductors, the manufacture of thinchips is required.

An example technique whereby the bottom surface of a silicon substrateis ground to obtain a thin semiconductor chip is disclosed in JapanesePatent Laid-Open Publication No. Hei 7-302769.

The following manufacturing method is disclosed in this publication.

A diffusion layer and an electrode are formed on the top surface of asilicon substrate, and while the bottom surface is ground using agrindstone, a crystal defect layer is introduced. Titanium, Monel andsilver are deposited, in the named order, on the bottom surface, to formthe crystal defect layer and obtain an ohmic electrode.

As the objective of this publication, an ohmic electrode is obtained byusing a grindstone having a large grain size to intentionally introducea crystal defect.

Generally, a semiconductor chip is sealed using a resin, and isattached, at its bottom surface, to an assembly board. According to theabove described manufacturing method, since, a crystal defect layer isdeposited on the bottom surface of the semiconductor chip, an ionizedcontaminant from the assembly board can be prevented from entering thesemiconductor chip through its bottom surface. However, a contaminantthat has passed through the resin, can not be prevented from enteringthe semiconductor chip at a side surface.

SUMMARY OF THE INVENTION

It is, therefore, one objective of the present invention to providemeans for at least preventing a contaminant from entering a thin-filmsemiconductor at a side surface and, more preferably, for alsopreventing the contaminant from entering through the bottom surface ofthe chip.

For a semiconductor device according to the present invention, a defectlayer for gettering a contaminant is formed on the side surfaces of asemiconductor chip.

More preferably, a defect layer for gettering a contaminant is formed onthe bottom surface and the side surfaces of a semiconductor chip.

As described above, since the defect layer is at least deposited on theside surfaces of the semiconductor chip, a contaminant passed through anassembly apparatus or another member can be prevented from entering thesemiconductor chip at its side surfaces, or at the bottom and the sidesurfaces, of the chip.

According to the present invention, as described above, a semiconductorchip can be protected from a contaminant, such as metal ions, during theassembly processing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a semiconductor chip according to a firstembodiment of the present invention;

FIGS. 2A and 2B are diagrams showing a method for manufacturing apackage that employs the semiconductor chip of the first embodiment;

FIG. 3 is a diagram showing the continuation of the manufacturing methodshown in FIG. 2;

FIG. 4 is a diagram showing a modification of the first embodiment; and

FIG. 5 is a diagram showing a semiconductor device according to a secondembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention will now be describedin detail while referring to the accompanying drawings, so as to moreclearly define the above objective and other objectives, the featuresand the effects of the present invention.

FIG. 1 is a diagram showing a semiconductor chip according to a firstembodiment of the present invention.

A crystal defect layer 2, for gettering a contaminant of metal ions,such as copper ions, is deposited on the side and the bottom surfaces ofa semiconductor chip 1.

The presence of the crystal defect layer 2 prevents a contaminant fromentering the semiconductor chip 1 through its side surfaces and itsbottom surface.

FIGS. 2A, 2B and 3 are diagrams showing a method for manufacturing asemiconductor device according to the present invention. Themanufacturing method will now be explained.

As shown in FIG. 2A, a diffusion layer, a source and gate electrodes anda circuit (none of them shown), which are components of a nonvolatilememory cell, are deposited on the top surface of an 800 μm thicksemiconductor substrate 3 made, for example, of silicon. Then, apassivation film 4, made of SiN or SiON, for example, is deposited onthe top surface of the resultant substrate 3. Since a fine nitride filmis employed as the passivation film 4, a heavy element, such as a copperion, can not pass through it. Next, the bottom surface of thesemiconductor substrate 3 is mechanically ground, using a grindstone,until the thickness thereof is, for example, 110 to 120 μm.

A grindstone should be selected that has a grain size large enough toform a crystal defect layer 2 on the bottom surface of the semiconductorsubstrate 3. The crystal defect layer 2 is a gettering layer forcapturing a contaminant, such as a copper ion. Thereafter, thesemiconductor substrate 3 is cut, using a blade cutter or a lasercutter, to separate the semiconductor chip 1, and the side surfaces ofthe chip are ground, using the grindstone, to obtain the crystal defectlayer 2 for the side surfaces (see FIG. 2B). It should be noted that solong as a defect layer that can capture a contaminant has already beenobtained for the side surfaces of the semiconductor chip 1 when thesemiconductor substrate 3 is cut using the blade cutter, the mechanicalgrinding process may not be performed. Further, a blade used forgrinding the bottom surface and a blade used for cutting out thesemiconductor chip 1 may have the same sharpness, and a blade #2000, forexample, is employed. In this case, the side and the bottom surfaceshave about the same roughness. This processing is employed tomanufacture the semiconductor chip 1.

As is shown in FIG. 3, the semiconductor chip 1 is mounted on the topsurface of an assembly board 6 using mounting tape 11. Then, a pad 8 onthe semiconductor chip 1 and a pad 9 on the assembly board 6 areelectrically connected by a wire 10. And thereafter, a sealing resin 5is applied to seal the semiconductor chip 1. Finally, soldering balls 7are attached to the bottom surface of the assembly board 6. Thisprocessing is employed to obtain a BGA (Ball Grid Array) package.

The assembly board 6 is a printed board fabricated by gluing a copperfoil to an insulating plate composed of a non-conductive material. Theprinted wiring for the assembly board 6 is then formed by patterning thecopper foil. Thereafter a solder resist coating is applied to allportions of the top surface of the printed board 6 other than theprinted wiring to which the wire 10 is soldered. Since copper isdiffused in the solder resist, the copper ions in the solder resist arediffused during the assembly process shown in FIGS. 2 and 3. Accordingto the invention, however, since the crystal defect layer 2 has beendeposited on the bottom surface of the semiconductor chip 1, the copperions are captured by the crystal defect layer 2 and are prevented fromentering the semiconductor chip 1. And although the copper ions arediffused throughout the sealing resin 5 and reach the side surfaces ofthe semiconductor chip 1, they are absorbed by the defect layerdeposited on the side surfaces of the semiconductor chip 1 and areprevented from entering the semiconductor chip 1. Further, since thepassivation film 4 has been formed on the top surface of thesemiconductor chip 1, the entry of copper ions through the top surfacecan also be prevented.

According to this embodiment, an explanation has been given for anon-volatile memory; however, the present invention is effective forother charge storage memories. That is, it is possible to prevent theoccurrence of a charge storage failure caused by a contaminant, such ascopper ions, that deteriorates the charge storage characteristics. Anexample charge storage memory can be a flash memory or a DRAM memory.

FIG. 4 is a diagram showing a modification of the first embodimentwherein semiconductor chips of the invention are laminated to constitutean MCP (a Multi Chip Package). This package is an assembly composed ofsemiconductor chips, such as a flash memory, an SRAM and a DRAM. Asemiconductor chip 1, for example, is a flash memory, and asemiconductor chip 12 is a DRAM. It should be noted that mounting tape11 is not shown in FIG. 4.

FIG. 5 is a diagram showing a semiconductor device according to a secondembodiment of the present invention.

A semiconductor chip 1 is mounted on an assembly board 6 using amounting member 12 that contains silver, so that the entire bottomsurface of the semiconductor chip 1 is covered with the mounting member12.

By employing the silver-containing mounting member 12, a Schottkybarrier is formed between the entire bottom surface of a semiconductordevice 3 and the mounting member 12. And since copper ions are veryheavy, so long as the Schottky barrier is present, copper ions from theassembly board 6 can not pass the barrier and enter the semiconductorchip 1.

A manufacturing method used to produce this semiconductor device is asfollows.

The semiconductor chip 1 is securely mounted on the assembly board 6 byusing the silver-containing mounting member 12,,so that the entirebottom surface of the chip 1 is covered with the mounting member 12.Since the other processes are the same as those in FIGS. 2 and 3, nofurther explanation for them will be given.

The present invention is not limited to these embodiments, and it isobvious that the embodiments can be variously modified within the scopeof the technical idea of the invention. For example, a semiconductordevice employing both the first and the second embodiments can also beprovided. That is, a semiconductor device is also available wherein acrystal defect layer is deposited on the bottom surface of thesemiconductor chip shown in FIG. 5, and the Schottky barrier ispositioned between the defect layer and the assembly board. Furthermore,although in the second embodiment a mounting member containing silver isemployed to form the Schottky barrier, so long as a Schottky barrier canbe formed, another metal may be employed.

1. A semiconductor device of a charge storage type wherein a getteringlayer is formed on the side surfaces and the bottom surface of asemiconductor chip.
 2. A semiconductor device according to claim 1,wherein a gettering layer is a crystal defect layer.
 3. A semiconductordevice according to claim 1, wherein the bottom surface of thesemiconductor chip is fixed to an assembly board using mounting tape. 4.A semiconductor device comprising: a semiconductor chip; and an assemblyboard, wherein the semiconductor chip is mounted on the assembly boardso as to at least form a Schottky barrier across the entire bottomsurface of the semiconductor chip.
 5. A semiconductor device wherein adefect layer for capturing a contaminant is at least formed on sidesurfaces of a semiconductor chip.
 6. A semiconductor device comprising:a semiconductor chip; a gettering layer formed on the side surfaces andthe bottom surface of the semiconductor chip; a resin layer that coversthe semiconductor chip; and an assembly board provided for the bottomsurface of the semiconductor chip by using a mounting member.
 7. Asemiconductor device manufacturing method comprising the steps of:forming a semiconductor element on the top surface of a semiconductorsubstrate; grinding the bottom surface of the semiconductor substrate;cutting the semiconductor substrate along the sides for a semiconductorchip; and forming a gettering layer on the bottom surface and the sidesurfaces of the semiconductor chip.
 8. A semiconductor devicemanufacturing method according to claim 7, whereby the gettering layeris deposited on the bottom surface of the semiconductor chip at a stepof securing the bottom surface to an assembly board using ametal-containing mounting member, so as to form a Schottky barrieracross the entire bottom surface.